# Robert Seifried's research while affiliated with Technische Universität Hamburg and other places

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## Publications (161)

Compared to conventional robots, flexible manipulators offer many advantages, such as faster end‐effector velocities and less energy consumption. However, their flexible structure can lead to undesired oscillations. Therefore, the applied control strategy should account for these elasticities. A feedforward controller based on an inverse model of t...

Classical particle dampers suffer from their non-robust damping behavior, i.e. they can only be efficiently applied to a specific frequency range and amplitude range. The reason for that is that particle motion, also called motion mode, and damper efficiency show a strong correlation. By changing particle or container properties the motion modes ar...

The development of modern mechatronic systems is often driven by the desire for more efficiency and accuracy. These requirements not only result in more complex system designs, but also in the simultaneous development of improved control strategies. Therefore, control of multibody systems is an active field of research. This contribution gives an o...

A modified robust design optimization approach is presented, which uses the first-order second-moment method to compute the mean value and the standard deviation for arbitrary objective functions. Existing approaches compute the gradient of the variance using the adjoint method, direct differentiation or finite differences, respectively. Adjoint fo...

With the rise in new soft robotic applications, the control requirements increase. Therefore, precise control methods for soft robots are required. However, the dynamic control of soft robots, which is required for fast movements, is still an open topic and will be discussed here. In this contribution, one kinematic and two dynamic control methods...

A multilevel design toolchain is used for the development of particle dampers for vertical transient vibrating structures. Thereby various experimental tests and numerical models are combined. The design toolchain consists of three levels. The first level deals with the micro-mechanical behavior of single particle–particle and particle–wall impacts...

The dynamics and the performance of a novel multibody wave energy converter
is investigated, which is based on inclined single modules connected
to a frame. The frame floats on the sea surface and the modules each move
translationally along inclined guidance rods. Direct-drive linear generators
or rotation based generators convert the relative tran...

Detailed impact simulations in flexible multibody systems can be simulated based on reduced isogeometric analysis (IGA) models. However, a precise simulation of an impact requires a high element resolution in the contact area. Usually in IGA, global refinement methods are used, which are easy to implement. However, in the literature, also the use o...

This paper explores the applicability of machine learning techniques for the generation of tailored wave sequences. For this purpose, a fully convolutional neural network was implemented for relating the target wave sequence at the target location in time domain to the respective wave sequence at the wave board. The synthetic training and validatio...

Compared to conventional robots, flexible manipulators offer many advantages, such as faster end-effector velocities and less energy consumption. However, their flexible structure can lead to undesired oscillations. Therefore, the applied control strategy should account for these elasticities. A feedforward controller based on an inverse model of t...

One of the biggest challenges in converting wave energy is to enable the use of low frequency waves, since the highest waves in typical sea states have low frequencies, as can be seen from the corresponding wave spectra, such as the Pierson–Moskowitz or JONSWAP spectra. In this paper, we show that this challenge is indeed achievable for the operati...

We apply the concept of servo constraints to end-effector trajectory tracking control of parallel robots with structural link flexibilities. Such servo constraints deliver the inverse robot model where solution approaches via projections are proposed, which transform the resulting differential-algebraic equations to ordinary differential equations....

In the estimation of future investments in the offshore wind industry, the operation and maintenance (O&M) phase plays an important role. In the simulation of the O&M figures, the weather conditions should contain information about the waves' main characteristics and the wind speed. As these parameters are correlated, they were simulated by using a...

In this contribution, an intelligent controller is proposed for an underactuated overhead container crane subject to both parameter uncertainties and unmodeled dynamics. The adopted approach is based on the sliding mode method to confer robustness against modeling inaccuracies and external disturbances. Additionally, an adaptive fuzzy inference sys...

The energy dissipation in sinusoidally driven particle dampers is highly dependent on the motion mode of the particle bed. Especially, for applications of low acceleration intensity, i.e., acceleration amplitude below gravitational acceleration, only small energy dissipation rates are obtained so far, due to sticking of particles. Here, a new and m...

In many granular processes, impacts play a crucial role. These impacts are often described by the coefficient of restitution (COR). This COR does not only depend on impact velocity but also on the material pairing, the shape of impacting bodies, number of impacts, etc. This paper analyzes and compares the sensitivity of the COR for often seen mater...

The dynamics of a novel wave energy converter based on a guided inclined point absorber are investigated. Thereby, it is studied through simulations and experiments whether different inclination angles of the guided point absorber lead to larger motion amplitudes and velocities in regular and irregular waves, from which energy can be harvested. For...

In structural optimization, the level set method is known as a well-established approach for shape and topology optimization. However, special care must be taken, if the design domains are sparsely-filled and slender. Using steepest descent-type level set methods, slender structure topology optimizations tend to instabilities and loss of structural...

Usually detailed impact simulations are based on isoparametric finite element models. For the inclusion in multibody dynamics simulation, e.g., in the framework of the floating frame of reference, a previous model reduction is necessary. A precise representation of the geometry is essential for modeling the dynamics of the impact. However, isoparam...

A novel approach for the computation of hydrodynamic forces due to random nonlinear water waves acting on a cylindrical pile is presented. This approach is based on paths of fluid particles underneath of solutions to the nonlinear Schrödinger equation (NLS). This is computationally very efficient compared to the determination of the corresponding s...

For precise control of soft robots soft sensors are required to measure the current configuration of the robot. In this contribution a new simple, accurate and easy to fabricate soft optical curvature sensors is presented. The optical sensor is based on the light loss along several polymer optical cable (POF) pieces which are lined up. This include...

Soft material robots are an emerging and fast-growing field of research [1] with potential application in various technical fields. These applications include, but are not limited to medical applications and all sorts of human-machine-interaction. Due to the soft structure, conventional components and design methodologies are not applicable. For re...

Object throwing is an efficient approach for overcoming the kinematic workspace limitations of robots in placement scenarios. Throwing of objects with rigid link robots has been widely studied in literature. Although using robots with spring-like flexible links can significantly increase the throwing distance, existing contributions are very rare....

Detailed impact simulations in flexible multibody systems are usually based on isoparametric finite element models. For modeling the dynamics of an impact, a precise representation of the geometry is essential. However, isoparametric finite elements involve the discretization of the geometry.
This work tests the isogeometric analysis (IGA) as an al...

Particle damping is a promising damping technique for a variety of technical applications. However, their non-linear behavior and multitude of influence parameters, hinder currently its wide practical use. So far, most researchers focus either on determining the energy dissipation inside the damper or on the overall damping behavior when coupled to...

End-effector trajectory tracking of a highly flexible three-link parallel robot is combined with collision avoidance in real-time. Typical real-time collision avoidance algorithms issue commands on actuator level which can cause large oscillations within flexible robots. Thus, the needed evasive motion at the points which are about to collide is us...

We consider tracking control for multibody systems which are modeled using holonomic and non-holonomic constraints. Furthermore, the systems may be underactuated and contain kinematic loops and are thus described by a set of differential-algebraic equations that cannot be reformulated as ordinary differential equations in general. We propose a cont...

Particle damping has become a favorable passive damping technique for lightweight structures, however, its complex dimensioning process hinder its wide use in technical applications. In this paper, a multilevel design tool chain is presented to enable a systematic design and dimensioning process of particle dampers. Thereby various numerical models...

Real-time end-effector trajectory tracking is applied to a newly developed parallel robotic system with two highly flexible links. In contrast to previous works, which are typically based on offline precalculations or rigid model inversion, a dynamic flexible multibody model is inverted online. As the underactuated system is non-minimum phase, the...

Usually, dynamical systems can be described by differential equations. An accurate model is essential when designing and optimizing a controller. However, not every system can be modeled easily by physical models due to highly nonlinear behavior, such as friction or backlash. Then, a data based approach, such as machine learning, might be helpful....

Flexible robots are often non‐minimum phase systems. Thus, their inverse model must be computed by stable inversion. Here, a simplification to the stable inversion process is proposed, which enables its application to complex underactuated multibody systems. As an example, a flexible manipulator modeled by the absolute nodal coordinate formulation...

For large‐scale topology optimization of flexible multibody systems, only little results exist. This is due to the complexity of the modeling of the flexible bodies and the big effort to provide exact gradients. The considered flexible multibody systems can undergo both large nonlinear motions as well as small elastic deformations. Here, the flexib...

The nonlinear Schrödinger equation plays an important role in wave theory, nonlinear optics and Bose‐Einstein condensation. Depending on the background, different analytical solutions have been obtained. One of these solutions is the soliton solution. In the real ocean sea, interactions of different water waves can be observed at the surface. There...

Nowadays electric cars are in the spotlight of automotive research. In this context we consider data based approaches as tools to improve and facilitate the car design process. Hereby, we address the challenge of vibration load prediction for electric cars using neural network based machine learning (ML), a data-based frequency response function ap...

We consider tracking control for multibody systems which are modelled using holonomic and nonholonomic constraints. Furthermore, the systems may be underactuated and contain kinematic loops and are thus described by a set of differential-algebraic equations that cannot be reformulated as ordinary differential equations in general. We propose a cont...

Particle damping is a passive damping technique at which granular material is either filled in a box attached to a vibrating structure or it is filled in holes embedded in the vibrating structure. Due to the structural vibrations, momentum is transferred to the granular material which interacts with each other. As a result, energy is dissipated by...

Particle dampers showa huge potential to reduce undesired vibrations in technical applications even under harsh environmental conditions. However, their energy dissipation depends on many effects on the micro- and macroscopic scale, which are not
fully understood yet. This paper aims toward the development of design rules for particle dampers by lo...

The Dynamic Modeling and Analysis Toolbox DynManto is an acedemic Matlab code which allows the modeling, simulation and sensitivity analysis of spatial multibody systems. The kinematics of rigid and flexible bodies is described by the floating frame of reference formulation and the body properties are provided by standard input data files. In this...

Particle damping is a very promising passive damping technique, however, it is still rarely used in technical applications due to its complex dimensioning. An experimental model is developed in order to investigate the energy dissipation of the dampers regardless of the underlying structure. The testbed consists of a particle box with a free‐free b...

Particle damping has become a favorable passive damping technique for lightweight structures, however, its complex dimensioning process hinder its wide use in technical applications. An experimental based model and a numerical model are developed in order to investigate the energy dissipation of the dampers regardless of the underlying structure. T...

Underactuated mechanical systems are frequently encountered in several industrial and real-world applications such as robotic manipulators with elastic components, aerospace vehicles, marine vessels, and overhead container cranes. The design of accurate controllers for this kind of mechanical system can become very challenging, especially if a high...

We consider tracking control for multibody systems which are modeled using generalized coordinates. Utilizing the two-degree- of-freedom approach to controller design, we combine a feedforward with a feedback controller. The feedforward control input is computed using the method of servo-constraints, which relies on an inverse model of the system....

Sphere collision is considered to be one of the basic collision configuration, and it influences the accuracy of the collision motion analysis in multibody dynamics. Therefore, it is important to measure their impact property accurately. In general, various methods were used to measure the motion of the spheres during collision. In this study, elas...

The approximation of gradients with a multigrid approach is presented in the framework of flexible multibody systems, in which the flexible bodies are modeled using finite element method. For the cases where the number of design variables are high, for example, in topology optimization where the density of each element is chosen as a design variabl...

Lego Mindstorms is a popular platform to teach robotics in schools and colleges. Basic mechanical properties as well as programming concepts can be taught to students of various ages. However, there are limitations, for example the lack of a camera for vision‐based control which is fundamental for autonomous applications like self‐driving cars. Wit...

A completely new compliant lightweight robot is presented with a kinematic loop and a highly flexible link. It is explained how to model such parallel robots accurately but still computationally efficient. The elastic deformations are described with the floating frame of reference approach. For the flexible components this allows to use linear fini...

This paper presents two different ways of modeling a road vehicle for general vehicle dynamics investigation and especially to optimize the suspension geometry. Therefore a numerically highly efficient model is sought such that it can be used later in gradient-based optimization of the suspension geometry. Based on a formula style vehicle with doub...

A classical trajectory tracking control approach combines feedforward control with a feedback loop. Since both parts can be designed independently, this is called a two degree of freedom control structure. Feedforward control is ideally an inverse model of the system. In case of underactuated mechanical systems the inverse model often cannot be der...

The servo-constraints approach is an efficient method for computing inverse models of underactuated multibody systems. Underactuated multibody systems possess more degrees of freedom than independent control inputs. The inverse model can be used as a feedforward controller in a two degree of freedom control structure. Servo-constraints constrain th...

The topology optimization of members of flexible multibody systems is considered for energy-efficient lightweight design, where the gradient calculation has an essential role. In topology optimization of flexible multibody systems, where the function evaluations are very time consuming, the gradient information is necessary to accelerate the optimi...

In this paper, the system dynamics of an overhead crane are inverted by servo-constraints. The inversion provides a feedforward control for trajectory tracking of the system output. The overhead crane is inherently underactuated and modeled as a two-dimensional mechanical system with nonlinear system dynamics. Actuators are modeled as first-order s...

Cable robots are widely applicable for various industrial tasks, where accurate trajectory tracking of the end-effector is an essential control objective. This is especially challenging for underactuated cable robots since they possess less actuators than degrees of freedom. Trajectory tracking can be achieved by using an inverse model based on ser...

Lightweight robots can be advantageous when considering the lower energy consumption, the possibility to use smaller motors and the lower material cost. Nevertheless, in such lightweight structures non-negligible flexibilities are inherent which can lead to significant oscillations making the control more difficult. Within this research end-effecto...

For the efficient analysis and optimization of flexible multibody systems, gradient information is often required. Next to simple and easy-to-implement finite difference approaches, analytical methods, such as the adjoint variable method, have been developed and are now well established for the sensitivity analysis in multibody dynamics. They allow...

Anti-jerk controller are essential for drive comfort during load-changes, since they reduce undesired driveline oscillations. Hybrid electrified vehicles enable greater degree of freedom to control these oscillations due to the two actuators, namely internal combustion engine and electric machine. At the same time the more complex communication str...

Inverse dynamics methods are presented and analyzed in detail for the feedforward control of underactuated manipulators. Thereby, two different exact strategies are discussed: the standard stable inversion method, which relies on the formulation of a two-point boundary value problem, and an alternative optimization problem formulation, which does n...

The influence of the strain rate sensitivity of the yield stress on multiple impact of three identical spheres were examined by FEM analysis in this study. Firstly the influence on colliding behavior were investigated. Then, the influence on macro-characteristics such as maximum contact force, maximum deformation, coefficient of restitution were in...

The purpose of this paper is to investigate the micromechanical processes during impact as well as the related macro-mechanical restitution properties in a three body multiple impact system. Thereby, the microscale refers to the detailed processes during impact, while the macroscale refers to the overall dynamics of the impact system which is norma...

Light-weight robots are advantageous considering the low energy consumption and the low material cost. However, in light-weight structures significant oscillations can occur which make the control very challenging. Objective of this research is end-effector trajectory tracking of a parallel manipulator with flexible links. Hereby, only the manipula...

For an efficient approximation of the local and global deformation behavior, impact simulations using reduced elastic models can be performed. Modally reduced models require a large number of eigenmodes to capture all local deformation effects. For this reason, the use of static shape functions in the contact area is recommended. However, due to hi...

A comprehensive control approach is presented to reduce the vibrations of a parallel manipulator with a kinematic loop and two flexible links whereof the longer one can show significant oscillations. The control objectives are end-effector trajectory tracking and active vibration control. The system is modeled as a flexible multibody system and exa...

In recent years, topology optimization has been used for optimizing members of flexible multibody systems to enhance their performance. Here, an extension to existing topology optimization schemes for flexible multibody systems is presented in which a more accurate model of revolute joints and bearing domains is included. This extension is of speci...

Load changes in automotive powertrains may cause uncomfortable vibrations during vehicle acceleration. These driveline oscillations occur due to flexible and underdamped shafts. Furthermore, backlashes in the drive train represent hard nonlinearities and lead to challenges in control. Reducing vibration only by feedback control may destabilize the...

Structural optimization methods have been recently successfully applied in optimizing dynamical systems and lightweight ma- chines. The main goal is to reduce the mass of flexible members without deteriorating the accuracy of the system. In this paper, structural optimization based on topology optimization of members of flexible multibody system is...

Light-weight robots and manipulators stand out due to their very good weight-to-load ratio and a low energy consumption. Unfortunately, the light-weight design yields a lower stiffness, which results in undesired elastic deformations, especially during high-speed working motion. One way to limit these unwanted oscillations can be implemented with m...

Employing the floating frame of reference formulation in the topology optimization of dynamically loaded components of flexible multibody systems seems to be a natural choice. In this formulation the deformation of flexible bodies is approximated by global shape functions, which are commonly obtained from finite element models using model reduction...

Control of flexible multibody systems, such as flexible manipulators, is a challenging task. This is especially true if end-effector trajectory tracking is aspired. On the one hand, these systems require a large number of generalized coordinates to describe their dynamical behavior accurately. On the other hand, only a small subset of these values...

The paper deals with underactuated mechanical systems, featured by less control inputs m than degrees of freedom f, m < f, subject to m servo-constraints (specified in time outputs) on the system. The arising servo-constraint problem (inverse dynamics analysis) is discussed with an emphasis on the way the servo-constraints are realized, varying fro...

Meshless particle methods, a group of simulation approaches that gains attention in the recent years in engineering and physics, are in the focus of this article. By means of application examples from different engineering contexts, we demonstrate how such methods, especially smoothed particle hydrodynamics and the discrete element method can be us...

Topology optimization techniques are applied in most cases for static applications. However, recently topology optimization procedures for structures under dynamic loads have been the focus of several studies. In this work, a topology optimization scheme for flexible multibody systems using equivalent static loads and displacement fields is investi...

The analysis and discussions in the previous chapters show that a minimum phase system allows a much easier control design than a non-minimum phase system. For minimum phase systems feedback linearization is possible and the design of feedforward control is significantly simplified. However, the initial design of an underactuated multibody system m...

Nearly all real world engineering systems comprise some type of nonlinearity. For output trajectory tracking of systems with continuous nonlinearities feedback linearization and feedforward control based on exact model inversion are powerful modern control techniques. This chapter provides an introductional representation of feedback linearization...

Due to the many theoretical and practical challenges which underactuated multibody systems pose, they are a fascinating research field with increasing industrial relevance in modern machine design. Especially the appealing use of light-weight design techniques, which often include body elasticity or passive joints, require a thorough understanding...

In this chapter, the fundamentals of modeling and generation of the equation of motion using the Newton-Euler formalism is presented for rigid multibody systems. Its extension to flexible multibody systems using the floating frame of reference approach is also discussed. Thereby, the given presentation concentrates on a descriptive approach in orde...

The control strategies presented in the previous chapter for trajectory tracking of multibody systems originate in differential-geometric concepts developed for general nonlinear systems. These are based on an explicit coordinate transformation into the nonlinear input?output normal form. An alternative control design approach for multibody systems...

Very important cases of underactuated multibody systems are flexible multibody systems. The actuation of a multibody system occurs in many cases at its joints, and thus, the elastic degrees of freedom have no associated control input. Thus, elasticity naturally causes underactuation. Due to its high technical relevance in modern light-weight machin...